The Cooling System...Pushing It's Limitations

[keithb7]

I have experimented with the timing. I begin with a timing light. A couple degrees before TDC . Then dial it in by ear. Adjusting it just back a tad so there is no pinging under full throttle and heavy load. I’ve also experimented too far retarded. The starter labors more to start it. Performance is reduced when driving up the hill home. To far advanced and the pinging is heard. I think I’m in the sweet spot with timing. The hill home provides generous “test & tune” opportunities.  
 

I’m thinking I am out of time for any further experimenting this year. Cool fall Canadian weather has arrived. I have been busy, with no driving time lately. I was in Alaska last week….Talk about cool weather! I’ll be driving  my Plymouth more soon. I’ll reassess the situation but, ambient air is way down compared to July & August. The furnace will be on soon. I’m seeing that Momma is starting pull out blankets. 

[keithb7]

On 9/15/2022 at 8:10 PM, 9 foot box said:

   It’s possible that when the car was in storage, before you bought it, mice had moved into your muffler. You tried everything else.

I’’m doubtful. I think I’m getting great exhaust air flow. I have no way to test and provide data. We don’t have a mouse problem. I’d have to remove the muffler to inspect & verify. Engine makes very good power.
 

 A good thought but I am very reluctant to think mice set up a camp in there. I’ll keep it in mind. 
 

As mentioned my rad is not stock. It could be slightly undersized. Nor is my 237 engine stock in this car. 
 

A brand new stock type water pump was installed about 6 months before I rebuilt the engine. I tend to think its good. Again, no easy way of proving water flow. Anyone have ideas on ways to test coolant flow?
 

 

Edited September 17, 2022 by keithb7

[Sniper]

1 hour ago, keithb7 said:

I have no way to test and provide data.

 

An exhaust back pressure gauge would tell you

[wallytoo]

sort of been following, and have read the entire thread.

 

i don’t worry about the higher temps; the 251 in my 1.5 ton is happy running 190 to a smidge above 220.  put 100 miles on it yesterday, ran it hard at 2800 to 3000 rpm.  i guess with this big truck, and hauling stuff with it, i’m used to seeing the temp run close to 220 a lot of the time.  timing is set to 2* atdc, mechanical only, no vacuum on this distributer.  the cooling system holds around 17 quarts, so that might be a bit higher than what yours has.  oh, and stock 4-blade fan, no shroud.

[maok]

The perfect solution to your issue is,

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Move house to where there is flat terrain....:)

 

Or a bigger radiator.

[maok]

If you are maintaining 40mph then the fan is really getting in the way, air flow through the rad is not being assisted by the fan, at lower speeds, yes.

 

Best to direct air flow from the front to the rad if possible.

[keithb7]

By comparison my ‘38 Chrysler has no cooling system issues. Stock cooling system through out. Yet 251 ci oversized engine with .030 milled off the head.

Stock, it has a bigger fan than my Plymouth. 

 

For experimental reasons I took the thermostat out of my Chrysler at the peak of our summer heat.  Have not put it back in yet. 47F here this morning.  Could not get my temp past the 130F mark. I sought out and tackled a good sized hill, throttle wide open.  3rd gear. 35 mph.I got it up to 140F.  Time to put the thermostat back in.  My Chrysler’s cooling system is proven. 
 

We get Texas style temps up here in July & Aug. Yet add the mountain terrain. The old flatheads are really pushed to the limits. 
 

Edited September 18, 2022 by keithb7

[Sniper]

25 minutes ago, keithb7 said:

Stock, it has a bigger fan than my Plymouth

 

Out of curiosity, did you (can you?) run the Chrysler fan on the Plymouth to see if it would help?

[Los_Control]

I wonder how radiator size compares?

Just creating a number here .... Lets say your original honeycomb radiator holds 10 quarts of liquid.

Now a modern aluminum replacement replacement holds 10 quarts. .... Technically they are the same size?

 

I'm just guessing the original honeycomb radiator would do a better job then a replacement.

 

I also think a modern radiator will work just as well, if you go with the right size.

 

I agree using capacity as a measurement is over simplistic. There are single, double, triple row radiators .... I imagine your modern diesel truck you use to tow with has a triple row radiator.

 

I figure if you have room to add a spacer to your fan, you have room to go with a wider radiator.

If you already have a 3 row .... then maybe larger capacity would help.

 

The fan only helps at low speeds or stop lights. Modern cars use electric fans on a T-stat control .... At a long stop light you will hear the fan turn on or off as needed. The fan will have no effect when moving down the road .... imho.

 

As @wallytoo says, your engine with the bored cylinders, shaved head .... may just like to run on the warm side & be fine.

 

[keithb7]

I like all your input and comments. Keep it coming. I will attempt to illustrate for clarity. 
 

My 1938 Plymouth: 
Rad is not stock. A small bit narrower so it can fit further into the tapered nose come of the grill. Remember stock engine was 201 23”. It now has a 25” long 237 ci engine.  
 

The Engine sits on a slight front upward incline. Generally almost all old 6 cyl car engines sit like this in their cradle. The fan, bolted to engine, sits on same off-vertical axis. Bottom of fan further forward than top. 
 

A previous owner had the longer engine installed and the slightly smaller rad. The rad mounts were fabbed up so it sits perfectly vertical. So there is a larger gap between fan blade and rad at the top,  versus the bottom. See exaggerated illustration below. I measured a 1.5” gap at the top fan blade. 0.5” at bottom fan blade. 
 

The current fan diameter in the Plymouth is 15”. A stock old Mopar fan.  I installed a larger 17” diameter spare Mopar fan that I own. It fit. However keep in mind it was now closer to the bottom of the rad, compared to the top, due to said angle.  I started the engine. No interference. All good right? It drove fine under power. Yet going down a local hill, when you let off the throttle, engine totsional forces change. The drivetrain is now pushing the engine. Dynamic braking occurs as the engine compression resists the rear wheels pushing it. The rubber engine mounts flex, ever slightly. The engine moved just a hair forward as the drivetrain flexes. Just enough so that the larger 17” fan blade kisses the rad core. I pulled over. Too late. Coolant was spewing out of my new re-cored low hour, radiator. $200 later it was repaired and went back in the car. Along with the smaller 15” diameter fan. 
 

I have the option to fab up some upper rad mount extensions. Get the rad at the same angle of the fan. Closer at the top for better efficiency. You may understand why I am a bit gun shy to do that. If you can believe it, things do move. My engine mounts are decent and new.  See what happens when you try to outsmart a Mopar engineer? They got it right. 
 

I do have room for a larger capacity custom built rad. I figure build it thicker toward the grill. Away from the destructive fan. Larger capacity. Another row of cores is a good option. Get the curent rad on the same angle  as the fan. Get the bottom nudged forward a little bit. Get the top closer to the fan. Same angle as the fan blade.  Then I could utilize that 17” bigger fan. That may do it too, on the cheap. 

Sounds like a good winter project. Yet I have to wait until next July to test any improvements. 
 

Sorry about any confusion. I own 2 1938 Mopars. A Chrysler and a Plymouth. The Chrysler could create ice to appear in a hot coffee in the Sahara. The Plymouth boils it. 

 

 

Edited September 18, 2022 by keithb7

[Bryan]

Put a DIY shroud on that baby.

[Los_Control]

With the Chrysler & no T-stat, the water never stayed in the radiator long enough to heat up.  I saw the same thing with my truck just driving it in the yard ... Installed T-stat & maintains 180.

I do believe your Chrysler is also 25" so no difference there.

 

 

I see the difference is the bored cylinders = thinner mass & bigger pistons = more heat. ... nothing crazy

Then the shaved head = more compression which also creates more heat.   ..... nothing crazy.

The aftermarket radiator could be less then adequate.

 

I see the opposite thing happening to the Plymouth. The cooling capacity is too low, the coolant heats up beyond T-stat capacity.

The T-stat now never closes because it is beyond it's limitations. The coolant just continues to circulate never getting a chance to cool in the radiator with the T-stat is closed.

 

See what I mean about your 2 cars? ... The Chrysler stock radiator works so well it never has a chance to warm up without a T-stat to control it.

 

Your Plymouth with a T-stat & aftermarket radiator. You have a 180 T-stat? The coolant is above 180 so it never closes ... same as removing it.

The coolant never stays in the radiator long enough too cool ... so you are just circulating hot water.

 

Same issues many car builders run into. DDspeedshop will drop a 454 big block in a 57 chebby.

The only radiator he has in his stash is from a 6 cylinder 57 chebby .... so he uses it.

Gets the car driving then complains it is running hot like your Plymouth .... He said the radiator was too small when he installed it. .... Now he is satisfied with his work, he gets online & orders a proper 3 core radiator for it & problem solved.

 

[wallytoo]

i do think there's merit in running a "hotter" t-stat, for the very reason described by @Los_Control.  if the t-stat is allowed to close for even a short while, the radiator can eliminate some heat from the coolant more effectively than when the coolant just flows through the radiator.  it may not seem like it, but the temp might end up bouncing from 220 to 190 that way (with the stat), vs running at 220 or so all the time (without the stat)

[Sniper]

the longer some coolant is in the radiator "cooling off" the longer other coolant is in the engine "heating up".  It's, at best, a zero sum game there.

 

Time is really not a major factor in cooling efficiency, temperature differential is the number one factor in radiator efficiency.  Followed by the thermal transfer rate of the material the radiator is made of, this is why dirty radiators don't cool as well as they d when clean.

[Los_Control]

Just now, Sniper said:

the longer some coolant is in the radiator "cooling off" the longer other coolant is in the engine "heating up".  It's, at best, a zero sum game there.

I think this is the which came first, chicken or egg theory ....

 

I think a hot engine first needs cool 180 water to cool it.

But if all the water is over 200 then the radiator never gets a chance to cool it .... even if for only 30 seconds the T-stat closes .... I think it is obvious the T-stat has no control here.

 

I like @wallytoo idea also ... would be a simple test to install a 195 T-stat just to monitor if it can control the temps better? ..... Who knows, it may just maintain a steady 195 temp.

 

With @keithb7observation skills, would be easy to see if the different T-stats could maintain proper temps for longer times.

The 195 still may get eventually over run with 200 temps .... but it may maintain 195 temps for 1/2 hour, where 180 maintains for 1/4 hour?

 

The T-stat opening & closing is what allows the radiator to work & shoot cool water back to the engine when the T-stat opens. .... even if the T-stat only stays closed for 30 seconds, that allows the air flow through the radiator to cool it.

 

I think this would be a good experimentation on what @keithb7cooling system is actually capable of.

 

We all know the block is clean, parts are new ... I would feel silly if asking the heater core was plugged .... Just a simple case of to small of a radiator to do the job. .... I think if a 195 T-stat improves it, proves the radiator is too small.

[wallytoo]

16 hours ago, Sniper said:

the longer some coolant is in the radiator "cooling off" the longer other coolant is in the engine "heating up".  It's, at best, a zero sum game there.

 

Time is really not a major factor in cooling efficiency, temperature differential is the number one factor in radiator efficiency.  Followed by the thermal transfer rate of the material the radiator is made of, this is why dirty radiators don't cool as well as they d when clean.

 

edit:  you are of course correct.  it is all about the efficiency of the radiator, the fan, and the pump.  once operating temp has been reached, in the summer, that's where the coolant temp sits.

 

disregard below...

 

 

if that were the case, why run a thermostat at all, except during cold weather?  i certainly run t-stats in all of my vehicles, all year.  there may be some, but i'm not aware of car manufacturers that recommend not running a t-stat during the summer months.

 

yes, the coolant in the engine gets hot.  it's supposed to.  these sixes can tolerate 220 in a non-pressure system with no problem.  running a 195 or 200 stat might allow the radiator to bring the coolant temp below 195 or 200, so that when the stat opens, that lower temperature coolant brings the block coolant temperature below 195, even if only briefly; whereas with no stat, the block never gets below 200 or 210 or whatever.

 

i can only go by the mechanical gauge i installed, and it vacillates between about 190 and 224, running a 195 stat.  ymmv.

Edited September 19, 2022 by wallytoo

[maok]

The thermostat is there to set the minimum temp (ie 160, 170, 180, 195, etc) once the coolant temp rises above thermostat value, the thermostat cannot open (further) or close, so the temp keeps rising if the radiator and fan are not affective enough to reduce the temp.

[wallytoo]

how much clearance in your engine compartment?  maybe that's a factor?  my truck has significant space between the block/head and the sides and hood, so a lot of room to have air moving, even if it isn't moving fast.  weight isn't a factor, because i'm at 14,500 gvw, and you aren't, but my truck cannot move as fast as your '38.

 

 

 

my cooling system is still mostly original - radiator for sure, i changed the waterpump last year.   i do run the heater hoses from the block to the heater core, and i don't close them off in the summer, so i do get a bit of heat loss/cooling there, inside the cab.  oil is 10w-40 or 15w-40, full flow filter.

Edited September 18, 2022 by wallytoo

[keithb7]

@Los_Control said: I see the difference is the bored cylinders = thinner mass & bigger pistons = more heat. ... nothing crazy. Then the shaved head = more compression which also creates more heat.   ..... nothing crazy.

The aftermarket radiator could be less than adequate.

 

I do tend to agree that the smaller aftermarket radiator is likely under performing when ambient air temps are above 80F It probably cannot keep up. When ambient temps are lower, it can keep up. My two engine blocks are identical in bore. Chrysler Canada made all their 25" long blocks all the same. They were either 3 ⅜ bore for the 218 and 226 CI engine. Or 3 7/16 bore for 237, 251, 265 CI engine. The 265 block had a little less material at the bottom walls to allow more clearance for the longest stroke. My understanding is the only other difference between these various engine displacements is stroke length. Varied by con-rod length and crank throw length.

 

I simply bored my 3 ⅜ block to 3 7/16 bore. Making it a 237. It has the identical bore now to my 251 engine in my Chrysler. There is no difference between my Plymouth and Chrysler cylinder walls or piston weight.

 

My Plymouth coolant did run hot with a new perfectly functioning 180 thermostat once ambient air temps started to warm up this summer. I only took out the thermostat in August to learn if it may have been sticking closed and impeding flow. It made no difference when I took the thermostat out.  Actually by taking out the thermostat the engine takes longer to heat up. Meaning short trips around town, were more manageable.  Yet every trip up the hill home it was right on the boiling point by the time I made it to the garage door. With rad cap off, un-pressurized (again another test) she started to bubble and pop in the driveway right after I got home and turned the key off. Heat sink taking effect. Coolant not circulating. With the 7 psi cap on, it don't believe it ever did boil over.

 

I am struggling a bit to accept the theory that the thermostat needs to close for a bit, to allow the coolant in the rad to cool down. Depending on ambient air temps, the thermostat stays closed for a time until the coolant reaches the thermostat's specified temp. The thermostat then stays open unless the ambient air, and wind going through the rad cools the coolant below the thermostat rated temp. Then it closes again. I'd wager that during summer hot ambient temps, your thermostat is not closing much at all.  You have a radiator that is able to efficiently take the heat out of the coolant. Based on the rad's size and number of core rows, and flow rate. I am doubting the thermostat is playing any role once it opens in 90F weather,  you're climbing a big hill, full power, and the coolant is fully circulating. The rad and the fan is doing all the work. The water pump pushing coolant on its way. The air has to move through the rad. Lots of it.  A slower climb up a long steep hill on a hot day, traveling too slow for good air flow, a rad slightly too small, throttle down, not lugging, ignition timing right, and a fan that would very likely benefit from a shroud probably....Amounts to my situation.

 

 

Edited September 18, 2022 by keithb7

[keithb7]

Here you can see the angle of my nose cone. Rad space gets smaller, the farther forward you place it. 
 

 A pic of my engine bay space. 
 

 

 

 

 

[westaus29]

Hi Keith, just wondering if you have played with advancing timing a little to compensate for today's higher octane fuel? Retarded timing generates more waste heat. My 38 7 passenger never had a temperature issue despite having put a smaller standard 38 radiator in it. And we have a long haul up into the Darling Range from Pinjarra to Dwellingup that tested its ability to hold speed in top gear. But it managed ok. Of course our hills are not like yours, only 300m climb!

Edited September 19, 2022 by westaus29
spelling

[wallytoo]

keith - your bay is a bit smaller than what is in mine.  probably still big enough, with enough clearance, that the heat produced by the exhaust and block are moving on quickly enough.  seems the radiator is the place to be trying things..

 

how close to "normal" curvature is that top radiator hose from the t-stat housing?  it's fairly long, with a pronounced curve.  any way to shorten it?

Edited September 19, 2022 by wallytoo

[Adam H P15 D30]

On 9/17/2022 at 7:23 AM, keithb7 said:

Anyone have ideas on ways to test coolant flow?
 

 

Pull the upper radiator hose and run it, see how much it pumps out.  Might need to put the garden hose in the radiator to keep it at an acceptable level while testing.

Then replace that flexi hose with a molded hose...

[soth122003]

18 hours ago, Sniper said:

Time is really not a major factor in cooling efficiency, temperature differential is the number one factor in radiator efficiency.  Followed by the thermal transfer rate of the material the radiator is made of, this is why dirty radiators don't cool as well as they d when clean.

What Sniper said got me to thinking. (I know, I smelled smoke too, lol). What is the thermal transfer difference between brass and aluminum? Keith stated that his Chrysler is all original and his Plymouth has an after market rad. His Chrysler is fine but the Plymouth has some cooling issues. While I have a 48 Plymouth, the rad is original. The only time I had cooling problems was when the rad was sludged up.  After cleaning it my temp stays around 175 degrees. While we don't have hills here in Florida we do have ungodly temps during the summer.  Just throwing this out there as food for thought.

 

Joe Lee

[LazyK]

throwing this out. could the slight angle of the radiator be the problem?  air turbulence is already created by the grill and the slight angle of the radiator is an additional restriction to a straight thru flow